This invention relates to a control system for a gas burner and, in particular, to a control system for a pilot and main gas burner assembly.
The ubiquitous control system for gas fired appliances such as a water heater comprises a single control valve having a thermostatic actuator. The appliance commonly employs a pilot burner and a main burner, each of which have separate gas supply conduits extending from the first control valve. The first control valve is a unitary structure which has a thermostatically actuated valve member in the supply line to the main burner whereby the gas supply to the main burner responds to the temperature of the appliance, e.g., the temperature of water in the water heater. A flame sensor such as a thermocouple is mounted for direct contact of the flame generated by the pilot burner and the thermocouple is connected directly to a latching mechanism that includes an electromagnetic coil. The valve structure includes a spring biased, manually moveable push rod to unseat the valve member and move its magnet armature into the magnetic field of the electromagnetic coil where it is retained as long as the thermocouple continues to generate sufficient electromotive force from exposure to the flame at the pilot burner.
It is desirable to provide redundant shutoff valve means in the gas supply line to the main burner. The redundant valve means provides an increased safeguard against leakage of gas by a malfunctioning gas valve. It can also serve as a high temperature shut off by connection to a high temperature limit switch (ECO). Desirably, this second or redundant valve should only be operative in the event of a loss of flame at the burner assembly, thereby preventing any accumulation of an ignitable gas mixture. This redundant valve mechanism is particularly desirable for use with combustible gases of greater density than air, e.g., propane, butane, etc., since these gases do not readily disperse when released from the burner.